A method which has been used to increase the capacity of cellular communication systems is the concept of hierarchical cells wherein a macro-cell layer is underlayed by a layer of typically smaller cells having coverage areas within the coverage area of the macro-cell. In this way, smaller cells, known as micro-cells or pico-cells (or even femto-cells), are located within larger macro-cells. The micro-cells and pico-cells have much smaller coverage thereby allowing a much closer reuse of resources. Frequently, the macro-cells are used to provide coverage over a large area, and micro-cells and pico-cells are used to provide additional capacity in e.g. densely populated areas and hotspots. Furthermore, pico-cells can also be used to provide coverage in specific locations such as within a residential home or office.
The current trend is towards introducing a large number of pico-cells to 3G systems. For example, it is envisaged that residential access points may be deployed having a target coverage area of only a single residential dwelling or house. A widespread introduction of such systems would result in a very large number of small underlay cells within a single macro-cell.
However, underlaying a macro-layer of a 3G network with a pico-cell (or micro-cell) layer creates several issues. For example, the introduction of a large number of underlay cells creates a number of issues related to resource allocation and intercell interference management.
For example, spectrum and frequency planning is typically applied in cellular communication systems to manage resource allocation and interference between cells in order to ensure that different cells can coexist efficiently. However, such an approach is not practical for the introduction of a large number of dynamically allocated residential access points as this would require a very frequent frequency replanning thereby resulting in unacceptable management resource demands and unacceptable disruptions to the cellular communication system. Accordingly, it is desirable that the introduction of a new residential access point can be achieved with no or minimal planning effort and with minimal disruption.
The problem of introducing underlay cells is exacerbated for base stations which are intended to only support specific user equipments. Specifically, residential access points can be private base stations that are configured to support only a small group of specific identified user equipments. For example, a residential access point may have a limited list of user equipments that are subscribed to use the residential access point. E.g., a residential access point in a subscribers house may only be used by members of that subscriber's household.
A problem in such an arrangement is that the residential access point must be able to effectively support the subscribed user equipment within a given coverage area (e.g. the residence) while allowing non-subscribed user equipments to be effectively supported by another cell which specifically may be the macro cell covering the residential access point cell.
However, these requirements tend to be in conflict with each other and typically the introduction of a residential access point will degrade some macro cell performance for non-subscribed user equipments and will require detailed and labour intensive optimisation in order to reduce this degradation and provide an improved trade-off between the residential access point and macro cell performance.
Hence, an improved system would be advantageous and in particular a system allowing increased flexibility, facilitated introduction of new base stations, improved support and/or operation for base stations supporting only a subset of users, reduced interference, reduced requirement for manual configuration of base stations and/or improved performance would be advantageous.